The invention relates to a refrigerant compressor having a piston, which is movable back and forth in a cylinder, the cylinder having at its end wall a discharge opening closable by a discharge valve, into which opening a projection on the corresponding end face of the piston projects when the piston is located in the region of its end position.
Refrigerant compressors of that kind are widely used in domestic refrigerators and upright and chest freezers. In a situation of increasing environmental awareness, there have for some years been attempts to make such cooling devices of lower and lower energy consumption. Saving of energy can be achieved on the one hand by improved heat insulation, and on the other hand also by increasing the efficiency of the refrigerant compressors.
One method of increasing efficiency is to construct at the end face of the piston a projection which, in the region of the upper dead centre of the piston, that is to say when the end face of the piston is as close as possible to the end wall of the cylinder, projects into the discharge opening. By means of this projection the volume of gas remaining in the discharge opening is displaced. Without that projection, the volume of gas remaining there would merely be compressed and could subsequently expand again, which leads to energy loss because of a non-adiabatic process in the refrigerant. Such a projection is known, for example, from the compressor, type SC, manufactured by Danfoss. A similar arrangement is known from U.S. Pat. No. 5,149,254.
The projection has the disadvantage, however, that it affects the flow of the refrigerant through the discharge opening. In particular, in the end region of the movement the cross-section available for the flow can become relatively small, so that the gas flowing through is accelerated. The temperature of the gas rises correspondingly. After flowing through the discharge valve, eddies frequently form in the flow of gas, which lead to an increase in the impedance, causing higher energy consumption.
The invention is based on the problem of increasing the efficiency of a compressor.